Device for controlling the voltage supply to an electric load

ABSTRACT

A circuit for controlling the power supplied to a fluorescent lamp load from a source of A.C. voltage by means of controlled rectifiers. A pulse-type control voltage for adjusting the firing angle of the controlled rectifiers is produced in a control circuit comprising a transformer having a primary winding composed of two electrically interconnected windings having a common junction that is connected to one terminal of the A.C. supply Voltage and to one of the supply conductors for the load. The two ends of the primary winding are connected together via the controlled rectifiers and they are also connected to the second terminal of the supply voltage and to the second supply conductor for the load, respectively. A pulse-type signal is generated in the secondary winding of the transformer that is further modified and applied to the gate electrodes of the controlled rectifiers to control the firing angle thereof.

'Oct. 14. 1969 P. CAILLEUX ET AL 3.473,085

DEVICE FOR CONTROLLING THE VOLTAGE SUPPLY TO AN ELECTRIC LOAD Filed May 9, 1967 2 Sheets-Sheet l n; LJJTORS PHILIPPE CAILLEUX BY CLAUDE MOTHIRON AG T P. CAILLEUX ETAL DEVICE FOR CONTROLLING THE VOLTAGE SUPPLY Oct. 14,19 9

TO AN ELECTRIC LOAD 2 Sheets-Sheet 2 Filed May 9, 1967 INYENTORb PHILIPPE CAILLEUX CLAUDE MOTHIRON United States Patent 61 Int. Cl. Gf 1 /02; H05b 37/02 US. Cl. 315-194 7 Claims ABSTRACT OF THE DISCLOSURE A circuit for controlling the power supplied to a fluorescent lamp load from a source of A.C. voltage by means of controlled rectifiers. A pulse-type control voltage for adjust-ing the firing angle of the controlled rectifiers is produced in a control circuit comprising a transformer having a primary winding composed of two electrically interconnected windings having 'a common junction that is connected to one terminal ofthe A.C. supply 'voltage and to one of the supply conductors for the load. The two ends of the primary winding are connected together via the controlled rectifiers and they are also connected to the second terminal of the supply voltage and to the second supply conductor for the load, respectively. A pulse-type signal is generated in the secondary winding of the transformer that is further modified and applied to the gate electrodes of the controlled rectifiers to control the firing angle thereof.

The present invention relates to apparatus for controlling the ignition of gas discharge devices or the like, and more particularly to a device for adjusting the power supplied to a fluorescent lamp by means of controlled rectifiers.

It is known that for all practical purposes the light intensity of a discharge lamp, particularly of a fluorescent lamp, can not be reduced by adjusting the amplitude of the supply voltage because the difference between the operational voltage and the quenching voltage is small, that is to say, of the order of 20%, which corresponds to a comparatively small reduction of the light flux. Moreover, the stable operation of the discharge in the lamp requires a voltage which exceeds the voltage drop across the lamp, while the stabilization of the discharge is obtained by employing an impedance connected in series with the discharge lamp, usually termed a ballast.

In order to control the light intensity it is possible to act upon the starting instant of the discharge in the lamp during each half period of the alternating supply. The flickering resulting therefrom at a low level of light flux is reduced by the post-luminescence of the powder on the inner wall of the lamp.

The starting instant of the discharge during each half period is, in general, determined by means of -a controldevice comprising a thyratron or a thyristor. The duration of the conduction of a thyristor or thyratron is controlled by a pulsatory auxiliary signal applied to an ignition electrodes or a control-electrode, the phase angles of said signal with respect to the supply voltage being controlled within suitable limits.

This auxiliary signal is obtained by means of a threshold control-member, for example, a double-base transistor (unijunction transistor). The control-electrode of the unijunction transistor is included in a circuit having a variable time constant and is supplied with voltage obtained by full-wave rectification of the supply volta e.

It has been found that with given control-devices, disturbances occur when the circuit of variable time constant 1s energized continuously. Moreover in the common lndustrial supply, the instantaneous voltage fluctuations have a fairly great amplitude and so produce corresponding fluctuations of the light flux. Particularly in the case of a weak light flux, this results in capricious instability Which has a particularly unpleasant physiological effect.

Various measures have been proposed to obviate this drawback. The French patent specification 1,321,112, for example, describes a light control-device having series impedances for limiting the discharge current and arranged so that, together with external means, they form resonant circuits which guarantee a constant luminous flux, even at a low light level. Though the purpose aimed at is achieved in this way, the design and manufacture of series impedances having characteristics deviating substantially from the conventional constructions always provide an economic disadvantage.

The known devices have the further disadvantage that the member for controlling the phase angle of the auxiliary signal, usually a potentiometer, exhibits a high voltage to ground so that special steps for insulation and safety are required, particularly in the case of remote control or automatic control by means of a photo-sensitive or thermo-sensitive member.

The present invention obviates these disadvantages.

A device according to the invention for controlling the power absorbed by a load supplied from an alternating voltage source, and provided with controlled rectifiers and an associated control-circuit for producing phase adjustable pulsatory control-voltages for the control-electrodes of the controlled rectifiers, features a transformer, having a primary winding which is divided into two elec trically interconnected portions. The junction of these portions is connected not only to one of the terminals of the supply source (first terminal) but also to one of the supply conductors of the load. The other end of the first portion of the primary winding of the transformer is connected to the second supply terminal and the other end of the second portion of the primary winding is connected to the other supply conductor of the load. The other ends of the first and the second portions of the primary winding of the transformer also are connected to each other through the controlled rectifiers. The controlcircuit of the controlled rectifiers is connected to the secondary winding of the transformer.

The voltage applied to the control-circuit is obtained from the voltage differences between the voltages across each of the primary half windings, that is to say from the difference between the voltage of the alternating-voltage source and the voltage derived therefrom by the controlled rectifiers. Subsequent to rectification and smoothing of the voltage across the secondary winding of the transformer, it is thus possible to produce pseudo-trapezoidal pulses of double the supply frequency. The pulse width is adjustable by controlling the duration of conduction of the controlled rectifiers.

These pulses are applied to the control-circuit of variable time constant and appear only when the controlled rectifiers are cut oil, thereby to accurately synchronize the instant when the load apparatus is switched on.

The term controlled rectifiers denotes not only a gas-discharge thyratron but also a thyristor. Although the device according to the invention is particularly suitable for the control of discharge lamps, it may, of course, also be employed for controlling the light flux of incandescent lamps, the power of electric heating systems or the speed of motors.

It is advantageous to connect the device according to the invention between the neutral lead and one phase of the alternating supply voltage, the neutral lead being connected to the central point of the primary winding of the transformer. By this measure and by the use of a coupling transformer between the control-circuit and the control-electrodes of the rectifiers, the device is insulated with respect to the supply so that the risk of accidents is limited and remote-control can be carried out without the need for special safety measures.

The invention will now be described more fully with reference to the accompanying drawing in which:

FIG. 1 shows the basic diagram of a device according to the invention;

FIGS. 2a, 2b and 2c illustrate the voltage waveforms at the terminals of the various windings of a transformer of a device shown in FIG. 1;

FIGS. 3a, 3b and 3c show the voltage waveforms across the control-circuit of the device shown in FIG. 1;

FIG. 4 shows the diagram of a practical embodiment of a device according to the invention, and

FIG. 5 shows the diagram of a photo-sensitive member suitable for use in a device according to the invention for automatic control of an illumination system.

The device shown in FIG. 1 comprises a transformer TR having a primary winding divided into two centrally interconnected halves P and P The free end of the primary half winding P is connected through a resistor R to the terminal 9 of one phase of the alternatingvoltage source. The common central point is directly connected to the terminals 8 and 10 of the voltage source and the load, respectively. Terminal 8 is connected to the neutral lead of the supply source. The free end of the primary half winding P is connected through a resistor R to the controlled phase of the output voltage (terminal 12).

With a View to the behaviour of the device in the starting period, it has been found to be advantageous to use the series resistors R and R They permit of equalizing, in opposite sense, the magnetic fluxes of the windings P and P of the transformer TR The secondary winding S of the transformer TR supplies the input voltage for a control-circuit 13. The control circuit produces switching pulses which are transferred through the primary winding P of a transformer TR having two secondary windings S and S to a device 14 comprising controlled rectifiers.

FIG. 2a illustrates, as a function of time t, one period of the alternating supply voltage U at the terminals 8, 9 of the primary half winding P of the transformer TR FIG. 2b illustrates the voltage U across the primary half winding P A portion of this voltage is cut oil? by the circuit 14, that is to say half of each half period. FIG. 20 illustrates the voltage U at the terminals of winding S resulting from the application of the voltages of FIGS. 2a and 2b in phase opposition to the transformer TR It will be obvious that the voltage U may be cut off at a different point from that shown in the figures by shifting the starting instant of the conduction period of the controlled rectifier of the circuit 14. Thus the width of the pulses forming said voltage is varied.

FIG. 3a illustrates again the signal U of FIG. 20. FIGS. 3b and 3c illustrate the signal U as a function of time t subsequent to rectification (U and smoothing (U The signal U is supplied to the circuit of variable time constant included in the control circuit 13.

In the practical embodiment of FIG. 4, the controlcircuit 13 includes a bridge rectifier formed by the diodes D D D and D The input of the circuit is connected to the secondary winding S of the transformer TR while the negative terminal is connected to the ground terminal 7. A Zener diode Z is connected with its anode to the negative terminal and with its cathode to the positive terminal of said bridge. The last-mentioned terminal is furthermore connected to the junction of a variable resistor R and a resistor R The other end of the resistor R is connected to one of the bases of a double-base transistor T The other end of the variable resistor R 4 is connected to the junction of the variable resistor R having a voltage-dependent resistance characteristic curve (VDR), and resistor R The other end of resistor R is connected to the negative terminal of the bridge. A resistor R is connected on the one hand to R and on the other hand to a terminal 4, which can be connected through a connecting member 6 to a terminal 5. A diode D is connected with its anode to the terminal 5 and with its cathode to the emitter of the transistor T A capacitor C is connected between the emitter of transistor T and the negative terminal of the rectifying bridge. The second base of the transistor T is connected to said negative terminal through the primary winding P of the pulse transformer TR The winding P is shunted by a diode D the anode of which is connected to the negative terminal. The terminal 1 and 2 of the resistor R and the terminal 3 connected to said negative terminal via an adjustable resistor R may be connected to a potentiometer 15. The ends of the potentiometer are connected to the terminals 1 and 3 and the tapping 16 is connected to the terminal 2.

The switching circuit 14 comprises the two thyristors TH and TH connected in parallel opposition between the terminals 9' and 12', which are connected to the terminals 9 and 12, respectively, through anti-interference inductors L and L which are magnetically coupled. The input terminal of the secondary winding S of the transformer TR is connected to the terminal 12 and the input terminal of the secondary winding S is connected to the terminal 9'. The other ends of S and S are connected to the control-electrodes of TH and TH respectively, through the resistors R and R A circuit formed by the series combination of the resistor R and the capacitor C is connected in parallel with the thyristors TH and TH A resistor R is connected between the output terminal 12 of the controlled phase and the neutral lead (terminals 8, 10).

The terminals 9' and 12 of the switching circuit 14 are connected through the resistors R and R respectively to the ends of the windings P and P of the transformer TR Between the terminals 8 and 9 a capacitor C is arranged. The capacitors C and C are connected between the terminal 7 and the terminals 9 and 8.

A fluorescent lamp L is energized via the series apparatus 17, formed by an auto-transformer TR having secondary heating windings S and and a primary winding P and by an inductor L and a capacitor C The common point 18 of windings S and P is connected to one of the terminals of the capacitor C the other terminal of which is connected to the junction of S and L The point 18 and the free ends 19 and 20' of P and L respectively, are connected to the terminals 10, 11 and 12, respectively.

The device according to the invention operates as follows. To one of the bases of the transistor T is connected the primary winding P of the pulse transformer TR The secondary windings S and S control the thyristors TH and TH When the potential of the charge on the capacitor C exceeds the threshold value of the transistor T the latter becomes conducting so that the discharge current of C passes through the winding P of the transformer TR As a result, a pulse is produced at the terminals of each of the secondary windings S and S and applied simultaneously to the control-electrodes of TH and TH via the equalizing resistors for the control-pulses R and R At this instant, only that thyristor whose cathode is negative and whose anode is positive becomes conducting. This conduction terminates at the instant when the polarity of the voltage applied to the terminals reverses. By varying the charging time of the capacitor C by means of the adjustable resistors R and R and the potentiometer 15, the instant of ignition of the thyristors TH or TH can be shifted with respect to the beginning of each half period of the supply voltage. The voltage required for charging the capacitor C is supplied, .sub-

sequent to rectification and smoothing, by the winding S of the transformer TR (see FIGS. 3a, 3b and 30).

If the FIGS. 2a and 2b illustrate the voltages across the windings P and P FIG. 2c shows that the secondary winding S of TR, will supply voltage only in the absence of current through the primary half winding P which means, when the thyristors are cut ofl during each half period.

The diode D serves to cut ofl? the positive voltage peaks of small amplitude during the intervals when the supply voltage for the control-circuit is suppressed. When the transformer TR is arranged at a distance from the device according to the invention, these voltages could be transferred to the connecting conductors of P and may produce a premature ignition of the double-base transistor.

The diode D serves to suppress the negative voltage peaks across the winding P due to the reaction of the voltages in the primary winding, produced at the extinction of the thyristors, alternately at the terminals of the two secondary windings. These voltages, by raising the voltage between the two bases of the transistor, might otherwise alter the operational conditions thereof.

The connecting portion 6 can be removed and a photosensitive element can be inserted in the charging circuit of C The effective or equivalent resistance of said element increases or decreases as a function of the incident light flux in accordance with the desired efiect.

If it is desired, for instance, to adapt the illumination of an underground passage to the level of the external light in order to avoid disagreeable transitions, it is suflicient to arrange, at the end of the tunnel, a photo-conductive cadmium sulphide resistor which is connected between the terminals 4 and 5, whereupon the fluctuation of the light produced by the fluorescent lamps follows the fluctuations of the external light under the control of the device according to the invention.

If it is desired to stabilize in a very simple manner the level of the illumination of a room having mixed illumination (natural light and fluorescent light), the device shown in FIG. 5 may be arranged between the terminals 4 and 5.

When the power of an electric heating system has to be controlled, stabilisation or adaptation of the heating may be achieved by using a resistor having a positive or negative temperature coefiicient, to which, if necessary, a transistor can be connected. A resistor having a positive temperature coelficient (PTC), arranged in a room heated by a heat generator operating under the control of the device according to the invention, is connected between the terminals 4 and 5 so that the temperature of the heated room is controlled. A resistor having a negative temperature coefiicient (NTC) connected between the terminals 4 and 5, exposed to the atmospheric temperature, provides automatically an increase in output power of the heating system when the atmospheric temperature drops.

Obviously, a PTC resistor may be connected in series between the terminals 4 and 5 in the heated room and an NTC resistor may be arranged outside, so that the two control methods are combined.

It will be evident to those skilled in the art that, when an amplifying transistor in common emitter connection is used, in conjunction with a thermally variable resistor, a higher control-sensitivity is obtained, which produces or does not produce an inversion of the sense of control depending upon the placement of the thermally sensitive element i.e., whether it is arranged between the emitter and the base or between the collector and the base. This inversion may be easily compensated for by appropriate choice of the polarity of the temperature coeflicient of the heat-resistive element.

From experiments it has been found that the use of a VDR instead of the resistor R is an important factor in the operation of the circuit of variable time constant, since in this way the control of the instant of ignition is linearized. The control range of the potentiometer 15 is thus enlarged and the control becomes more intense.

In order to compensate for any tolerances of the characteristics of the double-base transistors and VDRs, the circuit of variable time constant includes an adjustable resistor R A further adjustable resistor R accessible from the outside, permits the technician to adjust the minimum light flux for each particular use.

The circuit formed by R and C connected to the thyristors, protects them from brcak-down during the cut-01f period. Break-down might be caused by the appearance of transient voltages of high amplitude when a strongly inductive load circuit is switched on.

The two inductors L and L wound in opposite senses on a ferrite core, suppress the transient volt-age peaks appearing in some supply lines that otherwise cause arbitrary fluctuations of the light flux when the device is used for controlling fluorescent lamps. These inductors form, in addition, an effective protection against the propagation of radio disturbance through the conductors of the supply.

When the device is employed for controlling a plurality of fluorescent lamps, the resistor R suppresses current fluctuations that would occur upon the extinction of one of the lamps due' to the unavoidable tolerances of the characteristics of the fluorescent lamps.

The capacitors C and C between each of the conductors of the supply and ground and the capacitor C between the terminals of the supply serve to prevent the propagation of radio disturbances, produced by the switching effect of the device, along the conductors of the mains.

The lamp L is fed via a ballast 17. This ballast is formed by the auto-transformer TR having a winding P connected to the supply and the windings S and S for heating the electrodes of the lamp L. One of the supply conductors includes an inductor L A capacitor C improves the power factor of the ballast.

In a conventional ballast TR is an auto-transformer and the conductor 19 is connected to the conductor 20. When used in the device according to the invention, the conductor 18 is connected to the terminal 10 and the conductor 19 to the terminal 11 so that the filament wires of the lamp L can be energized in a normal manner.

The supply conductor 20 of the inductor L of the series apparatus is connected to the terminal 12, that is to say the controlled terminal of the device according to the invention.

To the terminals 4 and 5 of the control-device can be connected, by the terminals 24 and 25, the photo-sensitive member shown in FIG. 5. This photo-sensitive member comprises a transistor 26 of the pnp-type, the emitter of which is connected to the terminal 25 and the collector to the terminal 24. The potential of the base with respect to the emitter is derived from the voltage between the emitter and the collector by means of the photosensitive resistor 28, which forms a voltage divider with the adjustable resistor 27. The base of the transistor 26 is connected to the junction of the resistor 27 and 28. The photo-sensitive resistor 28, which is preferably formed by a cadmium sulphide cell, may be shunted by an adjustable resistor 29 in order to obtain a suitable working point for the device. The adjustable resistor 27 contributes to the setting of the working point of the arrangement and its sensitivity.

Such a photo-sensitive member with amplification does not require a separate voltage source and is supplied automatically by the charging current of the capacitor C of FIG. 4. When the resistor 28 is intensely illuminated, the ohmic resistance value is low so that the base and collector currents of the transistor 26 also are low. The equivalent resistance of the transistor 26 is then high. In the case of weak illumination, the equivalent resistance value of the photo-sensitive member is low so that a control member is obtained which automatically aifects the operation of the device of FIG. 4 to maintain an illumination of substantially constant level.

If, on the contrary, the illumination has to be matched to the level of a variable illumination, it is sufiicient to invert the positions of the resistors 27 and 28 in the arrangement. Preferably, resistor 29 then remains connected in parallel with the photosensitive resistor 28.

In order to control the supply of heat or to adapt it to the atmospheric conditions, it is sufiicient to replace, in the arrangement of FIG. 5, the photo-sensitive resistor 28 by an NTC or a PTC resistor, as described above.

Within the scope of the present invention, various modifications of the embodiments described above may be applied.

What is claimed is:

1. A device for controlling the power supplied to a load from an alternating current source, said device including controlled rectifier means and an associated control circuit for producing phase adjustable pulse type control voltages for the control electrodes of the controlled rectifier means, said device comprising first and second input terminals and first and second output terminals, a transformer having a primary winding and a secondary winding, said primary winding having first and second interconnected windings, means connecting the junction of the first and second windings to the first input terminal and the first output terminal, means connecting the other end of the first winding to the second input terminal and the other end of the second winding to the second output terminal, means connecting said controlled rectifier means between the said other ends of the first and second windings, and means connecting said control circuit to the secondary winding of the transformer, whereby said control circuit provides control pulses to render said controlled rectifier means conductive.

2. A device as claimed in claim 1 wherein the load comprises at least one discharge lamp and the controlled rectifier means comprises first and second controlled rectifiers connected in anti-parallel configuration.

3. A device as claimed in claim 1 wherein said input terminals are connected to said AC source and said first and second windings are wound in phase opposition to produce flux cancellation in the transformer whereby voltage pulses are produced in said secondary winding only during the time intervals that the controlled rectifier means are cut-off.

4. A device as claimed in claim 3 further comprising, a first resistor connected between said other end of said first winding and said second input terminal, and a second resistor connected between said other end of said second winding and said second output terminal.

5. A device as claimed in claim 1 wherein said control circuit comprises, a trigger device having its output coupled to the control electrodes of said controlled rectifier means, an RC network coupled to the input of said trigger device to control the operation thereof, means coupling said secondary winding to the input of said RC network, and means for adjusting the RC time constant of said RC network thereby to control the point of conduction of said trigger device and the firing angle of said controlled rectifier means relative to said AC source.

6. A device as claimed in claim 5 wherein said RC network includes a photosensitive element connected in series with the timing capacitor of said RC network and responsive to incident light energy so as to vary the time constant of said RC network as a function thereof.

7. A device as claimed in claim '6 wherein said controlled rectifier means comprises first and second controlled rectifiers connected in anti-parallel and said first and second windings are wound in phase opposition to produce flux cancellation in the transformer whereby voltage pulses are produced in said secondary winding only during the time intervals that the controlled rectifier means are cut-off, said device further comprising a resistor and capacitor serially connected in shunt with said first and second controlled rectifiers.

References Cited UNITED STATES PATENTS 3,358,186 12/1967 Nomura 315-194 I OHN W. HUCKERT, Primary Examiner R. F. POLLSSACK, Assistant Examiner US. Cl. X.R.

WIT," UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,473,085 Dated October 14, 1969 Inventofls) PHILIPPE CAILLEUX and CLAUDE MOTHIRON It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[- Column 1, line 54, after supply" insert voltage Column 4, line 16, change "terminal" (second occurrence) to terminals Column 4, line 18, cancel "R8" and insert R5 Column 5, line 71, cancel "resistive" and insert sensitive Column 6, line 32, cancel "mains" and insert supply Column 7, line 28, after "and" insert to Column 7 between lines 40 and 41, insert claims 3 as follows:

- A device as claimed in claim 1 wherein said first and second windings are wound in phase opposition to produce flux cancellation in the transformer whereby voltage pulses are produced in said secondary winding only during the time intervals that the controlled rectifier means are cut-off.

Renumber claims 3-7 as 4-8;

Column 8, line 4, change "3" to 4 Column 8, line 19, change "5" to 6 In the heading to the printed specification, line 12 "7 Claims should read 8 Claims.

Signed and Sealed this 24th day November 1970 J (SEAL) Amen:

Mil-M11.

m I. W. Amtmg I'm-11.11am 0f Patents 

